Micro-Electro-Mechanical Transducers

• US 20090140606A1
• Filed: 05/18/2006
• Published: 06/04/2009
• Est. Priority Date: 05/18/2005
• Status: Active Grant

• Current Assignee: Kolo Medical, Ltd.
• Original Assignee: Kolo Technologies, Inc.
• Inventors: Huang, Yongli
• Granted Patent: US 8,247,945 B2
• Time in Patent Office: Days
• US Class Current: 310/322
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: Y10T 29/49005 Acoustic transducer

Abstract

A micro-electro-mechanical transducer (such as a cMUT) is disclosed. The transducer has a substrate, a top plate, and a resilient structure therebetween. The resilient structure has multiple connectors distributed over the device element area to vertically transport the top player with distributed support. The resilient structure may be cantilevers formed using a middle spring layer covering cavities on the substrate. Connectors define a transducing space below the top plate. The resilient structure enables a vertical displacement of the connectors, which transports the top plate in a piston-like motion to change the transducing space and to effectuate energy transformation. No separate cells are necessary for each addressable transducer element. Multiple device elements can be made on the same substrate.

Claims

1. A micro-electro-mechanical transducer having a movable mechanical part to transform energy, the transducer comprising an addressable device element having a device element periphery defining a device element area, wherein the addressable device element comprises:

a substrate;

a top plate layer disposed above the substrate; and

a resilient structure between the substrate and the top plate layer, wherein;

(a) the resilient structure has a lower portion connecting to the substrate and an upper portion connecting to the top plate layer;

(b) the upper portion of the resilient structure has a plurality of connectors connecting to the top plate layer;

(c) the plurality of connectors are distributed over the device element area and have at least one connector located substantially away from the device element periphery toward an inner region of the device element area;

(d) the top plate layer and the connectors define a transducing space below the top plate layer;

(e) the addressable device element has at least one transducing member to induce energy transformation; and

(f) the resilient structure enables a vertical displacement of the plurality of connectors to transport the top plate layer in a substantially vertical direction, thus changing the transducing space and activating the transducing member.

2. The micro-electro-mechanical transducer of claim 1, wherein the resilient structure comprises a middle spring layer placed over the substrate, the middle spring layer and the substrate defining at least one cavity inside the device element area, the cavity dividing the device element area into at least two opposing sides, at least one side having an anchor anchoring the middle spring layer, and wherein the plurality of connectors are each horizontally distanced from the anchor by a sufficient length to define a cantilever between the connector and the anchor.

3. The micro-electro-mechanical transducer of claim 2, wherein the top plate is placed over the plurality of connectors, each connector having a desired height standing from the top of the middle spring layer to separate the top plate from the middle spring layer to define the transducing space below the top plate layer.

4. The micro-electro-mechanical transducer of claim 2 wherein the substrate and the middle spring layer define a plurality of cavities dividing the device element area into segments each substantially smaller than the device element area.

5. The micro-electro-mechanical transducer of claim 4 wherein the plurality of cavities comprises a first plurality of extended cavities dividing the device element area into a plurality of islands, and wherein at least some of the islands anchor the middle spring layer.

6. The micro-electro-mechanical transducer of claim 5 wherein the first plurality of extended cavities comprises straight cavities that are substantially parallel to each other.

7. The micro-electro-mechanical transducer of claim 5 wherein the first plurality of extended cavities comprises circular cavities.

8. The micro-electro-mechanical transducer of claim 5 wherein the first plurality of extended cavities comprise circular cavities of decreasing sizes each containing the secular cavities of smaller sizes.

9. The micro-electro-mechanical transducer of claim 5 wherein the first plurality of extended cavities comprising circular cavities of similar sizes arranged side-by-side.

10. The micro-electro-mechanical transducer of claim 5 wherein the plurality of cavities comprises a second plurality of extended cavities, and wherein the second plurality of extended cavities crosses the first plurality of extended cavities to form a grid of cavities defining a plurality of discrete islands, wherein at least some of the plurality of discrete islands anchor the middle spring layer

11. The micro-electro-mechanical transducer of claim 2 wherein the substrate has a plurality of discrete simple cavities arranged side-by-side.

12. The micro-electro-mechanical transducer of claim 11 wherein each discrete simple cavity device the substrate into a respective inner island and a common outer portion.

13. The micro-electro-mechanical transducer of claim 2 wherein the at least one cavity and the corresponding anchor(s) together occupy at least half of the device element area.

14. The micro-electro-mechanical transducer of claim 2 wherein in the addressable device element the middle spring layer is a contiguous layer covering the at least one cavity and the corresponding anchor(s).

15. The micro-electro-mechanical transducer of claim 2 wherein the middle spring layer is a contiguous layer covering substantially the entire device element area.

16. The micro-electro-mechanical transducer of claim 2 wherein at least one cavity has an annular shape dividing the device element area into an inner island and an outer region.

17. The micro-electro-mechanical transducer of claim 16 wherein the inner island anchors the middle spring layer.

18. The micro-electro-mechanical transducer of claim 16 wherein both the inner island and the outer region anchor the middle spring layer.

19. The micro-electro-mechanical transducer of claim 2 wherein the two opposing sides of at least one cavity are two opposing anchors each anchoring the middle spring layer.

20. The micro-electro-mechanical transducer of claim 19 wherein at least one connector is located between the two opposing anchors and horizontally distanced from each of the two opposing anchors by a sufficient length to define two cantilevers connected head-to-head.

21. The micro-electro-mechanical transducer of claim 2 wherein the cavity has an annular shape, the middle spring layer covers the entire cavity, and the at least one connector is disposed around the annular shape directly above a middle area of the cavity to define a two-dimensional plane cantilever.

22. The micro-electro-mechanical transducer of claim 1 wherein the plurality of connectors define a connector density profile indicating an average connector density per area location, and the resilient structure has a spring strength corresponding to each connector as an exerting point, wherein the average connector density and the spring length combinedly define an effective spring intensity profile indicating spring strength per area location.

23. The micro-electro-mechanical transducer of claim 22 wherein the effective spring intensity is substantially uniform over the device element area.

24. The micro-electro-mechanical transducer of claim 22 wherein the effective spring intensity is significantly higher at area locations near a center of the device element area than locations near a perimeter of the device element area.

25. The micro-electro-mechanical transducer of claim 22 wherein the device element area comprises a first region and a second region, the first region having a first thickness of the top plate layer and a first effective spring intensity, and the second region having a second thickness of the top plate layer and a second effective spring intensity, the second thickness being smaller than the first thickness and the second effective spring intensity being less than the first effective spring intensity.

26. The micro-electro-mechanical transducer of claim 22 wherein the device element area comprises a perimeter surrounding a middle region, wherein the top plate layer is flexible near the parameter but rigid in the middle region, clamped at a perimeter sidewall and supported by at least one cantilever in the middle region.

27. The micro-electro-mechanical transducer of claim 1 wherein in the addressable device element the top plate layer has a thickness profile having at least two different thicknesses across the device element area.

28. The micro-electro-mechanical transducer of claim 27 wherein the at least two different thicknesses comprise a first thickness corresponding to a normal thickness of the top plate layer and a second thickness corresponding to a bottom thickness of a cavity formed on the top plate layer, the first thickness and the second thickness regularly alternating across the device element area.

29. The micro-electro-mechanical transducer of claim 1 wherein the top plate layer comprises a first material and a second material different from the first material.

30. The micro-electro-mechanical transducer of claim 29 wherein the first material comprises a plurality of segments divided by separation trenches and the second material spans over the trenches to mechanically connect segments and/or at least partially fills the separation trenches.

31. The micro-electro-mechanical transducer of claim 1 which is a capacitance micromachined ultrasonic transducer (cMUT), wherein the addressable device element has a top electrode on the top plate layer and a bottom electrode on either the resilient structure or the substrate.

32. The micro-electro-mechanical transducer of claim 31 wherein resilient structure comprises a middle spring layer, and the bottom electrode is on the middle spring layer.

33. The micro-electro-mechanical transducer of claim 32 wherein the middle spring layer comprises a conductive material to effectuate the bottom electrode.

34. The micro-electro-mechanical transducer of claim 31 wherein the top electrode is a separate conductive layer deposited on the top plate layer.

35. The micro-electro-mechanical transducer of claim 1 wherein the transducer comprises a plurality of addressable device elements.

36. The micro-electro-mechanical transducer of claim 35 wherein the plurality of addressable device elements are separated by a separation trench formed through at least part of the top plate layer.

37. The micro-electro-mechanical transducer of claim 35 wherein the substrate is a conductive wafer, the plurality of addressable device elements are insulated from each other by an embedded insulator formed on the substrate, and the embedded insulator comprises an insulation cavity having a desired overall thickness and being filled with a dielectric material.

38. The micro-electro-mechanical transducer of claim 35 wherein the substrate is a conductive wafer, and the plurality of addressable device elements are each insulated by an embedded insulator formed on the substrate, the embedded insulator comprising a patterned cavity containing solid lines of oxidized native material of the substrate.

39. The micro-electro-mechanical transducer of claim 35 wherein the substrate is a conductive wafer, and the plurality of addressable device elements are each insulated by an embedded insulator formed on the top plate layer, the embedded insulator comprising a patterned cavity containing solid lines of oxidized native material of the top plate layer.

40. The micro-electro-mechanical transducer of claim 1 wherein the addressable device element is addressed from a back side of the substrate via a through-wafer interconnect formed through the substrate.

41. The micro-electro-mechanical transducer of claim 40 wherein the substrate is a conductive wafer, and the through-wafer interconnect comprises an annular trench surrounding a through-wafer conductor made of a native material of the conductive wafer.

42. The micro-electro-mechanical transducer of claim 41 wherein the through-wafer interconnect further comprises a dielectric material filled into the annular trench to insulate the through-wafer conductor from rest of the substrate.

43. The micro-electro-mechanical transducer of claim 41 wherein the through-wafer conductor is positioned directly underneath the addressable device element.

44. The micro-electro-mechanical transducer of claim 1 which is a pMUT, wherein the transducing member comprises a piezoelectric member disposed on the top plate or the middle spring layer.

45. The micro-electro-mechanical transducer of claim 1 which is a mMUT, wherein the transducing member comprises a magnetic member disposed on the top plate layer.

46. The micro-electro-mechanical transducer of claim 1 wherein the top plate layer comprises holes formed therein.

47. The micro-electro-mechanical transducer of claim 46 wherein the holes have a size and location profile optimized for a desired rigidity/mass ratio of the top plate layer.

48. The micro-electro-mechanical transducer of claim 1 wherein the vertical displacement of the connector is limited to a maximum displacement no greater than the height of the transducing space.

49. The micro-electro-mechanical transducer of claim 48 wherein the maximum displacement of the connector is at least one third smaller than the height of the transducing space.

50. The micro-electro-mechanical transducer of claim 48 wherein the maximum vertical displacement of the connector is limited by a motion stopper disposed in the cavity.

51. The micro-electro-mechanical transducer of claim 1 wherein the top plate is significantly more rigid than the resilient structure and is substantially unbent when transported by the vertical displacement of the connector(s).

52. A micro-electro-mechanical transducer having a movable mechanical part to transform energy, the transducer comprising a substrate, a middle spring layer and a top plate layer arranged in that order such that a bottom side of the top plate layer faces a top side of the middle spring layer and a bottom side of the middle spring layer faces a front side of the substrate, wherein the transducer comprises at least one addressable device element defining a device element area of the substrate and a corresponding device element area of the top plate layer, each addressable device element having a transducing member and being further characterized in that:

(a) the device element area has at least one cavity between the substrate and the middle spring layer, each cavity being sidewalled by at least one anchor anchoring the middle spring layer;

(b) the middle spring layer covers at least a part of each cavity;

(c) at least one connector of a desired height disposed above each cavity, the connector standing from the top of the middle spring layer;

(d) the top plate is placed over the connector(s) to define a transducing space below the top plate layer;

(e) each connector is horizontally distanced from one of the at least one anchor by a sufficient length to define a cantilever between the connector and the anchor, wherein the cantilever and the cavity enable a vertical displacement of the connector to transport the top plate layer substantially vertically, thus changing the transducing space and activating the transducing member; and

(f) the at least one cavity and the corresponding anchor(s) together occupy at least half of the device element area.

53. The micro-electro-mechanical transducer of claim 52, wherein at least one cavity is in an inner area of the substrate and divides the substrate into at least two segments.

54. The micro-electro-mechanical transducer of claim 52 wherein at least one cavity has an annular shape dividing the substrate into an inner island and an outer region.

55. The micro-electro-mechanical transducer of claim 52 wherein the cavity is sidewalled by two opposing anchors each anchoring the middle spring layer, and the at least one connector is located between the two opposing anchors and horizontally distanced from each of the two opposing anchors by a sufficient length to define a bridge containing two cantilevers connected head-to-head.

56. The micro-electro-mechanical transducer of claim 52 wherein the cavity has an annular shape, the middle spring layer covers the entire cavity, and the at least one connector is disposed around the annular shape directly above a middle area of the cavity to define a two-dimensional plane cantilever.

57. A micromachined ultrasonic transducer (MUT) structure comprising a substrate, a middle spring layer and the top plate layer arranged in that order such that a bottom side of the top plate layer faces a top side of the middle spring layer and a bottom side of the middle spring layer faces a front side of the substrate, wherein the MUT structure comprises a plurality of addressable MUT elements each defined by a MUT element area of the substrate and a corresponding MUT element area of the top plate layer, each of the plurality of addressable MUT element having a transducing member and being further characterized in that:

(a) the MUT element area has at least one cavity between the substrate and the middle spring layer, each cavity being sidewalled by at least one anchor anchoring the middle spring layer;

(b) the middle spring layer covers at least a part of each cavity;

(c) at least one connector of a desired height disposed above each cavity, the connector standing from the top of the middle spring layer;

(d) the top plate is placed over the connector(s) to define a transducing space below the top plate layer;

(e) each connector is horizontally distanced from one of the at least one anchor by a sufficient length to define a cantilever between the connector and the anchor, wherein the cantilever and the cavity enable a vertical displacement of the connector to transport the top plate layer substantially vertically with a piston-like motion, thus changing the transducing space and activating the transducing member; and

(f) the at least one cavity and the corresponding anchor(s) occupy at least half of the MUT element area.

58. The MUT structure of claim 57 wherein the plurality of addressable MUT elements are separated by a separation trench formed through at least part of the top plate layer.

59. The MUT structure of claim 57 wherein the separation trench is sealed using a sealing material.

60. The MUT structure of claim 59 wherein the sealing material is a sealing layer placed over top of the separation trench.

61. The MUT structure of claim 57 wherein the substrate is a conductive wafer, and the addressable MUT element is addressed through a through-wafer interconnect comprising an annular trench surrounding a through-wafer conductor made of a native material of the conductive wafer.

62. The MUT structure of claim 61 wherein the through-wafer conductor is positioned directly underneath the addressable MUT element.

63. The MUT structure of claim 57 which is a cMUT structure, wherein the transducing member comprises a top electrode located on the top plate layer and a bottom electrode located either on the middle spring layer or the substrate.

64. The MUT structure of claim 63, wherein the middle spring layer is a silicon layer, and the bottom electrode comprises a highly doped region on the middle spring layer.

65. The MUT structure of claim 57 wherein the top plate layer comprises holes formed therethrough, the holes having a size and location profile that is optimized for a desired rigidity/mass ratio of the top plate layer.

66. The MUT structure of claim 57 further comprising an integrated circuit built in the top plate layer.